Contact-discharge truing/dressing method and device therefor

ABSTRACT

A contact-discharge truing/dressing method and a device therefor, capable of very simply conducting truing/dressing of a superabrasive grindstone, especially a superabrasive grindstone having a metal binder. The contact-discharge truing/dressing method brings a rotated conductive grindstone into contact with a pair of electrodes to which a DC voltage or pulse voltage is applied, and subjecting the conductive grindstone to an intermittent truing/dressing by contact discharge produced when opening/closing a circuit of a positive electrode, electrode chips, a grindstone binder, electrode chips, a negative electrode, and parts of the side surfaces of dual-ring rotary electrodes insulated by an insulation layer being used as a pair of electrodes.

TECHNICAL FIELD

The present invention relates to a method and device forcontact-discharge truing/dressing through the use of dual-ring rotaryelectrodes.

BACKGROUND ART

The superabrasive grindstone has low wear compared with conventionalgrindstones, and is suitable for high-precision shape creating work. Onthe other hand, because of the difficulty of its truing/dressing, thesuperabrasive grindstone is presently not in widespread use.

Out of superabrasive grindstones, with respect to a conductivegrindstone using metal or the like as a binder, a technique such asdischarge truing/dressing or electrolytic dressing is applied (see TheJournal of The Society of Grinding Engineers, Vol. 39, No. 5, 1995, SEP,pp. 21-22, and pp. 25-26). However, any conventional method has been amethod executed in a liquid, and has been unsuitable for a dry grindingmachine, which prevails in the mold manufacturing industry. Theaforementioned method has not been simple because it has needed to use abrush to supply power to the main shaft of a grindstone.

In contrast, there is a contact-discharge truing/dressing method whereina voltage is applied to a pair of electrodes with an insulatinggrindstone sandwiched therebetween, wherein the electrodes are ground bya conductive grindstone, and wherein a contact-discharge phenomenonoccurring at this time is utilized (see The Journal of The Society ofGrinding Engineers, Vol. 39, No. 5, 1995, SEP, p. 24). This method issimple because it does not need to use a brush to supply power to themain shaft of a grindstone.

However, in these conventional contact-discharge truing/dressingmethods, because the electrodes are ground while keeping constant thedepth of cut of the grindstone with respect to the electrodes and thefeed speed of the electrodes, no stable contact-discharge phenomena havebeen achieved, and in some cases, a problem that periodicalirregularities have occurred over the circumference of the grindstoneworking surface has sen (see 1990, The proceedings of The Japan Societyfor Precision Engineering, Spring Conference, pp. 933-934.) Also, sincethe electrodes have been ground largely in a mechanical fashion, wear ofthe electrodes has been heavy. In addition, this contact-dischargetruing/dressing method cannot be applied to a nonconductive grindstone.

There are several other truing/dressing methods wherein abrasives arecaused to fall off by mechanically shaving away a binder (this isusually a binder other than metal), using a conventional grindstonerotated (see The Journal of The Society of Grinding Engineers, Vol. 39,No. 5, 1995, SEP, pp. 8-11).

However, when being applied to dry grinding, any method has caused aproblem in that large quantities of flying abrasives adversely affectthe lifetime of a machine tool and human bodies. Moreover, since thetruing/dressing according to these methods relies upon a mechanicalforce, a problem has occurred in that, when attempting to create a sharpV-shaped edge shape, the edge becomes chipped.

In any of the above-described truing/dressing methods, no measures havebeen taken to conduct truing/dressing while monitoring the circularityof a grindstone. As a result, it has been impossible to continuously andautomatically execute the transition of the truing/dressing conditionfrom the rough truing/dressing condition to the finish truing/dressingcondition. Furthermore, it has been impossible to determine whileconducting truing/dressing, at what point of time the truing/dressing isto be ended.

In addition, in any of the above-described truing/dressing methods, nomeasures have been taken to conduct truing/dressing while monitoring thedecreasing amount of the radius of a grindstone, due to the truing. As aconsequence, in in-process truing/dressing, it has been impossible toperform working while correcting the tool path.

DISCLOSURE OF INVENTION

As described above, any conventional truing/dressing method has involvedvarious problems.

In view of such circumstances, the present invention aims to provide acontact-discharge truing/dressing method and a device therefor capableof very simply performing truing/dressing of a superabrasive grindstone,especially a superabrasive grindstone having a metal binder.

In order to achieve the above-described object, the present inventionprovides:

-   [1] a contact-discharge truing/dressing method, comprising the steps    of bringing a rotated conductive trued/dressed grindstone into    contact with a pair of electrodes to which a DC voltage or pulse    voltage is applied, and subjecting the conductive trued/dressed    grindstone to an intermittent truing/dressing by contact discharge    produced when opening/closing a circuit comprising a positive    electrode, electrode chips, a grindstone binder, electrode chips,    and a negative electrode, parts of the side surfaces of dual-ring    rotary electrodes insulated by an insulator being used as a pair of    electrodes.-   [2] a contact-discharge truing/dressing method, comprising the steps    of bringing a rotated nonconductive trued/dressed grindstone into    contact with a pair of electrodes to which a DC voltage or pulse    voltage is applied, and subjecting the nonconductive trued/dressed    grindstone to an intermittent truing/dressing by contact discharge    produced when opening/closing a circuit comprising a positive    electrode, electrode chips, and a negative electrode, parts of the    side surfaces of dual-ring rotary electrodes insulated by an    insulator with a thickness of several hundred μm or less being used    as a pair of electrodes.-   [3] a contact-discharge truing/dressing device wherein a rotated    conductive trued/dressed grindstone is brought into contact with a    pair of electrodes to which a DC voltage or pulse voltage is    applied, and wherein the conductive trued/dressed grindstone is    subjected to an intermittent truing/dressing by contact discharge    produced when opening/closing a circuit comprising a positive    electrode, electrode chips, a grindstone binder, electrode chips,    and a negative electrode, the contact-discharge truing/dressing    device including dual-ring rotary electrodes insulated by an    insulator, and a pair of electrodes comprising parts of the side    surfaces of the dual-ring rotary electrodes.-   [4] a contact-discharge truing/dressing device wherein a rotated    nonconductive trued/dressed grindstone is brought into contact with    a pair of electrodes to which a DC voltage or pulse voltage is    applied, and wherein the nonconductive trued/dressed grindstone is    subjected to an intermittent truing/dressing by contact discharge    produced when opening/closing a circuit comprising a positive    electrode, electrode chips, and a negative electrode, the    contact-discharge truing/dressing device including dual-ring rotary    electrodes insulated by an insulator with a thickness of several    hundred μm or less, and a pair of electrodes comprising parts of the    side surfaces of the dual-ring rotary electrodes.-   [5] the contact-discharge truing/dressing device set forth in [3] or    [4] further comprising a drive mechanism for driving the dual-ring    rotary electrodes in the rotating shaft direction thereof.-   [6] the contact-discharge truing/dressing device set forth in [3],    [4], or [5] further comprising a structure capable of applying a    voltage between dual-ring rotary electrodes with mutually different    diameters.-   [7] the contact-discharge truing/dressing method set forth in [1] or    [2] wherein the contact-discharge is performed in an environment of    a liquid, a mist, or the air.-   [8] the contact-discharge truing/dressing method set forth in [1] or    [2] wherein, in order to remove initial rotational deflections of    the side surfaces of the dual-ring rotary electrodes, after the side    surfaces of the electrodes have been ground by the trued/dressed    grindstone without applying a voltage between the electrodes,    truing/dressing is started with a voltage applied between the    electrodes.-   [9] a contact-discharge truing/dressing method, comprising the step    of obtaining, using the device set forth in [3], [4], or [5], a    predetermined shape of the edge of a grindstone, by providing the    electrodes with a feed in the rotating shaft direction thereof in a    state in which a predetermined angle is formed between the rotating    shaft of the electrodes and that of the trued/dressed grindstone.-   [10] a contact-discharge truing/dressing method, comprising the step    of disposing, using the device set forth in [3], [4], or [5], a    drive device for the dual-ring rotary electrodes, on a    numerical-control moving table having a crosswise movement mechanism    and a rotational mechanism, to thereby perform high-precision form    truing/dressing.-   [11] a contact-discharge truing/dressing method, comprising the step    of inserting, using the device set forth in [3], [4], or [5], a    contact-discharge current limiting resistor and a current detector    on the side of the power supply circuit of the device so as to be in    series with the pair of electrodes, whereby the feed speed of the    dual-ring rotary electrodes in the rotating shaft direction thereof    is numerically controlled so that the power consumption between the    electrodes becomes the maximum when the contact-discharge current    takes on the peak value I_(p), that is, so that the peak current    value I_(p) becomes I_(p)=E/(2R) where the power supply voltage is E    and the series resistor is R.-   [12] the contact-discharge truing/dressing method set forth in [11]    wherein the mean value I_(m) and the peak value I_(p) of the output    from the current detector are acquired at a period of one or more    revolutions of the trued/dressed grindstone, and wherein    truing/dressing is performed while estimating the circularity of the    trued/dressed grindstone, based on the value of I_(m)/I_(p).-   [13] the contact-discharge truing/dressing method set forth in [12]    wherein, based on the estimated circularity of the trued/dressed    grindstone, the magnitude of contact-discharge power consumption    E·I_(p)/2 is automatically adjusted by a numerical control or an    automatic control to thereby perform high-precision truing/dressing.-   [14] the contact-discharge truing/dressing method set forth in [12]    wherein, when the estimated circularity of the trued/dressed    grindstone becomes a predetermined value or less, the    truing/dressing is automatically ended.-   [15] the contact-discharge truing/dressing method set forth in [11]    wherein, in order that a control is performed more stably, the kind    of the applied voltage to the dual-ring rotary electrodes is    automatically switched between the DC voltage and pulse voltage.-   [16] a contact-discharge truing/dressing method, comprising the step    of disposing, in the contact-discharge truing/dressing device set    forth in [3], [4], or [5], a displacement sensor for measuring the    positions of the side surfaces of the electrodes, on the    side-surface side of the electrodes to thereby perform    truing/dressing while measuring the truing amount.-   [17] the contact-discharge truing/dressing device set forth in [3],    [4], or [5] further comprising a displacement sensor for measuring    the positions of the side surfaces of the electrodes, the    displacement censor being provided on the side-surface side of the    electrodes.-   [18] the contact-discharge truing/dressing method set forth in [16],    wherein the contact-discharge truing/dressing method is applied to    in-process truing/dressing to thereby execute the method while    correcting the tool path based on the truing amount.-   [19] the contact-discharge truing/dressing method set forth in [1]    or [2], wherein a grindstone is disposed inside the dual-ring rotary    electrodes, and wherein adherents of the electrode material adhering    to the trued/dressed grindstone are removed for every discharge.-   [20] the contact-discharge truing/dressing method set forth in [1]    or [2], wherein a grindstone is disposed outside the dual-ring    rotary electrodes, and wherein adherents of the electrode material    adhering to the trued/dressed grindstone are removed for every    discharge.-   [21] the contact-discharge truing/dressing device set forth in [3]    or [4] further comprising a grindstone disposed inside the dual-ring    rotary electrodes.-   [22] the contact-discharge truing/dressing device set forth in [3]    or [4] further comprising a grindstone disposed outside the    dual-ring rotary electrodes.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a construction view showing an embodiment of acontact-discharge truing/dressing device according to the presentinvention.

FIG. 2 is a block diagram of an embodiment of a control device of thecontact-discharge truing/dressing device according to the presentinvention.

FIG. 3 is an explanatory view of an embodiment of a contact-dischargetruing/dressing method according to the present invention.

FIG. 4 is an enlarged view (Part 1) showing the portion A in FIG. 3 toexplain the truing/dressing mechanism thereof.

FIG. 5 is an enlarged view (Part 2) showing the portion A in FIG. 3 toexplain the truing/dressing mechanism thereof.

FIG. 6 is a construction view showing the main section of an embodimentof a contact-discharge truing/dressing device having an electrode feedmechanism according to the present invention.

FIG. 7 is a construction view showing an embodiment of a power supplymechanism of the contact-discharge truing/dressing device according tothe present invention.

FIG. 8 is a sectional view showing an example of dual-ring rotaryelectrodes with a diameter different from that of the contact-dischargetruing/dressing device shown in FIG. 7.

FIGS. 9A to 9C are explanatory views of various types ofcontact-discharge truing/dressing methods.

FIG. 10 is a representation of an embodiment of a method of the presentinvention for removing rotational deflections on the side surfaces ofthe electrodes according to the present invention.

FIG. 11 is a representation of an embodiment of a contact-dischargetruing/dressing method of the present invention for obtaining a V-shapedgrindstone edge shape.

FIG. 12 is a construction view showing an embodiment of acontact-discharge truing/dressing device of the present invention inwhich a drive device for the dual-ring rotary electrodes is disposed ona numerical-control moving table having a crosswise movement mechanismand a rotational mechanism.

FIGS. 13A and 13B are explanatory views of an embodiment of a method ofthe present invention for numerically controlling the feed speed of thedual-ring rotary electrodes in the rotating shaft direction thereof.

FIGS. 14A and 14B are explanatory views of an embodiment of a method ofthe present invention for estimating the circularity of a grindstone.

FIG. 15 is an explanatory view of an embodiment of a method of thepresent invention for automatically adjusting the magnitude ofcontact-discharge power consumption E·I_(p)/2 by a numerical control oran automatic control, based on the circularity of a grindstone.

FIG. 16 is an explanatory view of an embodiment of a method of thepresent invention for automatically ending contact-dischargetruing/dressing when the estimated value of the circularity of thegrindstone becomes a predetermined value.

FIG. 17 is an explanatory view of an embodiment of a method of thepresent invention for automatically switching the kind of the voltage tobe applied to the dual-ring rotary electrodes, between the DC voltageand pulse voltage, in order that a control is performed more stably.

FIG. 18 is an explanatory view of an embodiment of a method of thepresent invention for performing contact-discharge truing/dressing whilemeasuring the truing amount.

FIG. 19 is a representation of a modification of the method forperforming truing/dressing shown in FIG. 18.

FIG. 20 is an explanatory view of an embodiment of a contact-dischargetruing/dressing method according to the present invention that isapplied to in-process truing/dressing, and that is executed whilecorrecting the tool path based on the truing amount.

FIG. 21 is a representation of an embodiment of a truing/dressing deviceaccording to the present invention that has a dual-ring rotaryelectrodes inside which a conventional grindstone (nonconductivegrindstone) is disposed.

FIG. 22 is a representation of an embodiment of a truing/dressing deviceaccording to the present invention that has a dual-ring rotaryelectrodes outside which a conventional grindstone (nonconductivegrindstone) is disposed.

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, the embodiments of the present invention will be describedwith reference to the drawings.

FIG. 1 is a construction view showing an embodiment of acontact-discharge truing/dressing device according to the presentinvention. This is an example in which a dual-ring rotary electrode typecontact-discharge truing/dressing device system is applied to edgetruing of a grindstone for profile grinding. In order to facilitateunderstanding the drawing, in FIG. 1, the rotating shaft of thegrindstone for profile grinding and that of the dual-ring rotaryelectrodes are depicted so as to be perpendicular to each other. Inactuality, an angle of 30° was formed between these shafts in order toform the edge of the grindstone for profile grinding into a V-shape withan angle of 30°.

In FIG. 1, reference numeral 1 denotes a grindstone for profile grinding(trued/dressed grindstone), reference numeral 2 a base, referencenumeral 3 a front cover, reference numeral 4 an O-ring, referencenumeral 5 an O-ring pressing lid, reference numeral 6 a rear cover,reference numeral 7 a connector, reference numeral 8 a cover, referencenumeral 9 a handle, reference numeral 10 a front limiter, referencenumeral 11 a rear limiter, reference numeral 12 a motor bracket,reference numeral 13 a stepping motor, reference numeral 14 a coupling,reference numeral 15 a ball screw, reference numeral 16 a ball-screwsupport unit, reference numeral 17 a nut, reference numeral 18 a nutbracket, reference numeral 19 a main-shaft moving table, referencenumeral 20 linear guide rails, reference numeral 21 linear guidesliders, reference numeral 22 a motor bracket, reference numeral 23 a DCmotor, reference numeral 24 a coupling, reference numeral 25 a mainshaft, reference numeral 26 a main-shaft support unit, reference numeral27 a main-shaft auxiliary support unit, reference numeral 28 amechanical lock, reference numeral 29 an electrode holder, referencenumeral 30 an insulating layer, reference numeral 31 an outer ring ofthe dual-ring rotary electrodes, reference numeral 32 an insulatinglayer of the dual-ring rotary electrodes, reference numeral 33 an innerring of the dual-ring rotary electrodes, each of reference numerals 34and 35 a power-supply brush, reference numeral 36 a power-supply brushbracket, and reference numeral 37 a displacement sensor.

First, the structure of the dual-ring rotary electrode typecontact-discharge truing/dressing device is described with reference toFIG. 1.

The ball screw support unit 16 is fixed to the base 2, therebysupporting the ball screw 15 with a pitch of 1 mm. One end of the ballscrew 15 is connected to the rotating shaft of the stepping motor 13through the coupling 14, and is subjected to a rotational drive at astep angle of 0.1°. Here, the stepping motor 13 is fixed to the base 2by the motor bracket 12.

The nut 17 meshes with the ball screw 15, and is fed in the rotatingshaft direction by the rotation of the stepping motor 13. The nutbracket 18 is fixed to the nut 17, and when the nut bracket 18 pressesthe switch of the front limiter 10 or the rear limiter 11, the steppingmotor stops.

The two linear guide rails 20 extending in the rotating shaft directionof the electrodes are fixed to the base 2 in parallel with each other.The two linear guide sliders 21 are mounted on each of the linear guiderails 20. The main-shaft moving table 19 is fixed to the linear guidesliders 21 and the nut bracket 18, and is driven by the stepping motor13 in the rotating shaft direction of the electrodes.

The main shaft 25 is supported by the main-shaft support unit 26 and themain-shaft auxiliary support unit 27, which are fixed to the movingtable, and one end thereof is connected to the DC motor 23 forrotationally driving the main shaft 25 through the coupling 24. Here,the DC motor 23 is fixed to the main-shaft moving table 19 using themotor bracket 22.

Carbon (or copper) was used for an electrode material of the outer ring31 and the inner ring 33 of the dual-ring rotary electrodes, and anepoxy resin was used for the insulating layer 32 of the dual-ring rotaryelectrodes, which insulates the inner and outer rings. Here, thethickness of the insulating layer was set to about 500 μm. The dual-ringrotary electrodes and the electrode holder 29 are adhered to each otherby the insulating layer 30 comprising a thermoplastic resin with a highinsulation property. The dual-ring rotary electrodes comprising thedual-ring rotary electrode outer ring 31, the dual-ring rotary electrodeinner ring 33, and the dual-ring rotary electrode insulating layer 32,and the electrode holder 29, are fixed to the main shaft 25 by means ofthe mechanical lock 28.

The spring-loaded power-supply brushes 34 and 35 are in contact with theouter ring 31 and the inner ring 33 of the dual-ring rotary electrodes,thereby implementing power supply. These power-supply brushes 34 and 35are supported by the bakelite-made power-supply brush bracket 36 fixedto the main-shaft moving table 19. This embodiment is not one in which apower supplying method of certain embodiments of the present inventionis adopted.

The displacement sensor 37 is disposed on the table of the grindingmachine or the base 2, and monitors the edge portion of the grindstonefor profile grinding by measuring the positions of the electrode sidesurfaces.

FIG. 2 is a block diagram of an embodiment of a control device of thecontact-discharge truing/dressing device according to the presentinvention.

In FIG. 2, reference numeral 38 designates a discharge current limitingresistor, reference numeral 39 a hole current detector, referencenumeral 40 a numeric data processor, reference numeral 41 a digitalinput device, reference numeral 42 a digital output device, referencenumeral 43 an A/D converter, reference numeral 44 a D/A converter,reference numeral 45 a peak detecting circuit, reference numeral 46 alow-pass filter, reference numeral 47 a V/F converter, reference numeral48 a switching circuit, reference numeral 49 a Y-shaped relay, referencenumeral 50 a power amplifier circuit, reference numeral 51 a steppingmotor driver, each of reference numerals 52 and 53 an analog switch,reference numeral 54 a DC motor driver, reference numeral 55 a manualoperation device, and reference numeral 56 an amplifier.

Now the control device will be described with reference to FIG. 2.

For control, the numeric data processor 40 is used that comprises thedigital input and output devices 41 and 42, the A/D converter 43, andthe D/A converter 44.

As the power supply for a discharge circuit, the power amplifier circuit50 in a power operating amplifier is used, and the output voltage of thepower supply can be set by an instruction from the numeric dataprocessor 40. This makes it possible to continuously change the truingcondition from the rough truing condition to the finish truingcondition. Here, the output of the power amplifier circuit 50 iselectrically insulated from a commercial power supply and the ground forsafety.

The positive electrode of the power amplifier circuit 50 is directlyconnected to the power-supply brush 35. On the other hand, the negativeelectrode of the power amplifier circuit 50 is connected to the Y-shapedrelay 49 changeable by an instruction from the numeric data processor40, and the switching between the DC voltage and pulse voltage isperformed at the Y-shaped relay 49. When a pulse voltage is selected,the output passes through the switching circuit 48 comprising anelectric field effect transistor, and is then connected to thepower-supply brush 34 through the hole current detector 39 and thedischarge current limiting resistor 38. On the other hand, when a DCvoltage is selected, the output does not pass through the switchingcircuit 48. Here, the switching frequency of the switching circuit 48can be set by an instruction from the numeric data processor 40, byusing the V/F converter (voltage-frequency converter) 47.

The output from the hole current detector 39 is separated into threepaths and is taken in the numeric data processor 40. A first path is onefor directly taking in the output. A second path is one for taking inthe output after passing through the peak detecting circuit 45. The peakvalue I_(p) of the contact-discharge current is obtained from the signalvoltage of this second path. Upon receipt of an instruction from thenumeric data processor 40, the peak detecting circuit 45 is reset to aperiod of one or more revolutions of the grindstone. A third path is onefor taking in the output after passing through the low-pass filter 46.The mean value I_(m) of the contact-discharge current is obtained fromthe signal voltage of this third path.

The stepping motor 13 is driven in response to the output from the holecurrent detector 39. Specifically, the rotational speed and therotational direction of the stepping motor 13 are numerically controlledso that the power consumption between the electrodes becomes the maximumwhen the contact-discharge current takes on the peak value I_(p), thatis, so that the above-described peak current value I_(p) becomesI_(p)=E/(2R) where the power supply voltage is E. Also, when the frontlimiter 10 or the rear limiter 11 is pressed, an input pulse to thestepping motor driver 51 is shut down by the analog switches 52 or 53.The output signals from the front limiter 10 and the rear limiter 11 aresent also to the numeric data processor 40.

The startup and stop instructions, the switching of rotationaldirection, and the adjustment of rotational speed are all manuallyexecuted in the manual operation device 55. Only the signal line of thealarm output signal issued when something out of the ordinary takesplace in the DC motor 23, is connected to the numeric data processor 40,so that an emergency measure can be taken.

After being amplified by the amplifier 56, the output of thedisplacement sensor 37 is taken in the numeric data processor 40, and isused for monitoring the edge position of the grindstone 1 for profilegrinding (see FIG. 1).

FIG. 3 is an explanatory view of an embodiment of a contact-dischargetruing/dressing method according to the present invention, and FIGS. 4and 5 are enlarged views showing the portion A in FIG. 3 to explain thetruing/dressing mechanism thereof.

For example, as shown in FIG. 4, a dual-ring rotary electrodes 201comprising an electrode inner ring 202, an insulating layer 203, and anelectrode outer ring 204, is used. A DC voltage or pulse voltage isapplied between the electrode inner ring 202 and the electrode outerring 204, thereby rotating the dual-ring rotary electrodes 201. When thedual-ring rotary electrodes 201 is fed in the rotating shaft directionthereof, and the side surfaces thereof are brought in contact with theconductive grindstone 101, contact discharge occurs at the portions ofelectrode chips 220 and 221, in a circuit comprising the electrode outerring 204, the electrode chips 220, the conductive binder 102, theelectrode chips 221, and the electrode inner ring 202. The conductivebinder 102 is melted by the heat due to the above-described contactdischarge, so that abrasives 103 fall off. In the truing device shown inFIG. 4, the insulating layer 203 may have a thickness of several hundredμm or more.

In contrast, as shown in FIG. 5, if the thickness of the insulatinglayer 212 of the dual-ring rotary electrodes 201 is set to severalhundred μm or less, the present contact-discharge truing/dressing methodcan also be applied to the truing of the nonconductive grindstone 110.In this case, when the side surfaces of the dual-ring rotary electrodes201 are brought in contact with the nonconductive grindstone 110,contact discharge occurs at the portion of electrode chips 222, in acircuit comprising the electrode outer ring 213, the electrode chips222, and the electrode inner ring 211. The nonconductive binder 111 ismelted by the heat due to the above-described contact discharge, so thatthe abrasives 112 fall off. In this manner, reducing the thickness ofthe insulating layer between the electrodes allows the truing/dressingwith respect to a nonconductive grindstone, as well.

These methods are simple because they do not need to use a brush tosupply power on the main shaft of the trued/dressed grindstone 100. Inaddition, these methods allow the truing/dressing to be performed undera dry grinding condition, as well.

The control of the discharge power in the contact-discharge isimplemented as follows. As shown in FIG. 3, a discharge current limitingresistor R and a hole current detector A are inserted on the powersupply side so as to be in series with the pair of electrodes. In thiscircuit, when the current value I=E/(2R), the contact-discharge powerbecomes the maximum with respect to the power supply voltage E. Whenthere are deflections on the trued surface, the current I varies at therotational period of the grindstone 100. However, if the feed speed v ofthe electrodes in the rotating shaft direction thereof is controlled sothat the maximum value I_(p) of the current value I becomesI_(p)=E/(2R), it is possible to efficiently remove the largest portionof the deflections. Here, reference numeral 105 denotes a DC or pulsepower supply.

FIG. 6 is a construction view showing the main section of an embodimentof a contact-discharge truing/dressing device having an electrode feedmechanism according to the present invention.

As shown in FIG. 6, the present contact-discharge truing/dressing deviceis configured so that the dual-ring rotary electrodes 201 are fed in therotating shaft direction thereof by an electrode feed mechanism 120.Here, reference numeral 100 denotes a grindstone, and reference numeral105 denotes a DC or pulse power supply.

FIG. 7 is a construction view showing an embodiment of a power supplymechanism of the contact-discharge truing/dressing device according tothe present invention.

In FIG. 7, reference numeral 121 designates the rotational main shaft ofthe dual-ring rotary electrodes 201, reference numeral 122 a conductorring fixed to the aforementioned rotational main shaft 121, referencenumeral 123 an insulating layer, reference numeral 124 an electrodeflange, reference numeral 125 a washer, reference numeral 126 anelectrode fixing bolt for electrically interconnecting the rotationalmain shaft 121 and the electrode inner ring 202, reference numeral 127 apower-supply spring for electrically interconnecting the electrode outerring 204 and the electrode flange 124, and each of reference numerals128 and 129 a power-supply brush.

In this way, a power is supplied to the electrode inner ring 202 throughthe power-supply brush 128, the conductor ring 122, the rotational mainshaft 121, the electrode fixing bolt 126, and the washer 125, and issupplied to the electrode outer ring 204 through the power-supply brush129, the electrode flange 124, and the power-supply spring 127.

FIG. 8 is a sectional view showing an example of dual-ring rotaryelectrodes with a diameter different from those of the contact-dischargetruing/dressing device shown in FIG. 7.

As shown in FIG. 8, in this embodiment, there are provided dual-ringrotary electrodes 201′ with a smaller diameter.

FIGS. 9A to 9C are explanatory views of various types ofcontact-discharge truing/dressing methods according to the presentinvention. In FIGS. 9A to 9C, the contact-discharge operations performedin environments of a liquid, a mist, and the air, are respectivelyshown. In FIGS. 9A to 9C, the same parts as those in FIG. 3 aredesignated by the same reference numerals, and the descriptions thereofare omitted.

Specifically, as shown in FIG. 9A, when a contact-discharge operation isperformed in a liquid, a nozzle 301 for liquid supply is disposed at thecontact discharge position, and a contact-discharge is caused to takeplace while supplying a liquid 302.

Also, as shown in FIG. 9B, when a contact-discharge operation isperformed in a mist, a nozzle 303 for mist supply is disposed at thecontact discharge position, and a contact-discharge is caused to takeplace while supplying a mist 304.

Of course, as shown in FIG. 9C, a contact-discharge operation may beperformed in the air without supplying anything.

FIG. 10 is a representation of an embodiment of a method of the presentinvention for removing rotational deflections on the side surfaces ofthe electrodes.

As shown in FIG. 10, in order to removing initial rotational deflectionson the side surfaces of the electrodes 201, a switch 107 is turned off,and the side surfaces of the electrodes are ground by the trued/dressedgrindstone 100 without applying a voltage between the inner ring and theouter ring of the electrodes. Thereafter, with a voltage applied betweenthe inner ring and the outer ring of the electrodes, truing/dressingoperation is started.

FIG. 11 is a representation of an embodiment of a contact-dischargetruing/dressing method of the present invention for obtaining a V-shapedgrindstone edge shape.

In this embodiment, a predetermined edge shape of a grindstone can beobtained by providing a dual-ring rotary electrodes 405 with a feed inthe direction of a rotating main shaft 406 thereof, in a state in whicha predetermined angle θ is formed between the rotating main shaft 406 ofthe dual-ring rotary electrodes 405 and the rotating shaft 402 of agrindstone 401.

FIG. 12 is a construction view showing an embodiment of acontact-discharge truing/dressing device of the present invention inwhich a drive device for the dual-ring rotary electrodes is disposed ona numerical-control moving table having a crosswise movement mechanismand a rotational mechanism.

In this embodiment, a drive device for a dual-ring rotary electrodes 415is disposed on a numerical-control moving table 418 having a crosswisemovement mechanism and a rotational mechanism. Specifically, whencontact-discharge truing/dressing is performed by bringing the dual-ringrotary electrodes 415 into contact with a grindstone 410 fixed to agrindstone rotating shaft 411, a drive mechanism for the rotating mainshaft 416 of the dual-ring rotary electrodes 415, and consequently, themain body 417 of the truing/dressing device is disposed on thenumerical-control moving table 418 having the crosswise movementmechanism and the rotational mechanism. This makes it possible toperform high-precision form truing/dressing.

FIGS. 13A and 13B are explanatory views of an embodiment of a method ofthe present invention for numerically controlling the feed speed of thedual-ring rotary electrodes in the rotating shaft direction thereof,where FIG. 13A is a construction view of the present system, and FIG.13B is a waveform view of a current under a numeric control.

In this embodiment, a contact-discharge current limiting resistor R anda current detector A are inserted on the side of the power supplycircuit of this device so as to be in series with the dual-ring rotaryelectrodes 201, and the feed speed of the dual-ring rotary electrodes201 in the direction of the rotating shaft 121 is controlled by anumeric control device 501 so that the power consumption between thedual-ring rotary electrodes 201 becomes the maximum when thecontact-discharge current takes on the peak value I_(p), that is, sothat the above-described peak current value I_(p) becomes I_(p)=E/(2R)where the power supply voltage is E.

Thereby, it is possible to maintain the contact-discharge state verystable, and inhibit the periodical irregularities from occurring on theworking surface of the grindstone. Also, this reduces the ratio of theelectrode portion that is vainly ground in a mechanical fashion, therebydecreasing wear of the electrodes, which leads to the conservation ofwork environment in a clean state.

FIGS. 14A and 14B are explanatory views of an embodiment of a method ofthe present invention for estimating the circularity of a grindstone,where FIG. 14A is a construction view of the present system, and FIG.14B is a waveform view of a current under a numeric control.

In this embodiment, the mean value I_(m) and the peak value I_(p) of theoutput from the current detector A are acquired at a period of one ormore revolutions of the grindstone, and truing/dressing is performedwhile estimating the circularity of the grindstone, based on the valueof I_(m)/I_(p). Namely, there is provided a circularity estimatingdevice 602 for estimating the circularity of a grindstone, based on theI_(m)/I_(p) value. As shown in FIG. 14B, the larger the I_(m)/I_(p)value is, the higher the circularity of the grindstone is. Here,reference numeral 601 denotes a numeric control device for numericallycontrolling the electrode feed speed so that the peak value I_(p) of thecurrent I becomes I_(p)=E/(2R).

As described above, the mean value I_(m) and the peak value I_(p) of theoutput from the current detector A are measured at a period of one ormore revolutions of the grindstone, so that truing/dressing can beperformed while estimating the circularity of the grindstone, based onthe value of I_(m)/I_(p). Therefore, it is possible to automate thecontinuous transition of the truing/dressing condition from the roughtruing/dressing condition to the finish truing/dressing condition, aswell as the determination as to at what point of time thetruing/dressing is to be ended.

FIG. 15 is an explanatory view of an embodiment of a method of thepresent invention for automatically adjusting the magnitude ofcontact-discharge power consumption E·I_(p)/2 by a numerical control oran automatic control, based on the circularity of a grindstone.

In this embodiment, there is provided a contact-discharge powerautomatic adjustment device 610 that automatically adjusts thecontact-discharge power consumption E·I_(p)/2, based on the mean valueI_(m) and the peak value I_(p) of the output from the current detectorA, and high precision truing/dressing is performed by automaticallyadjusting the magnitude of the contact-discharge power consumptionE·I_(p)/2 by a numeric control or an automatic control, based on theestimated value of the circularity of the grindstone.

FIG. 16 is an explanatory view of an embodiment of a method of thepresent invention for automatically ending contact-dischargetruing/dressing when the estimated value of the circularity of thegrindstone becomes a predetermined value.

In this embodiment, there is provided an automatic ending processingdevice 620 that automatically performs end processing of thecontact-discharge truing/dressing when the estimated value of thecircularity of the grindstone becomes a predetermined value, wherebytruing/dressing can be automatically ended when the circularity of thegrindstone becomes a satisfactory value.

FIG. 17 is an explanatory view of an embodiment of a method of thepresent invention for automatically switching the kind of the voltage tobe applied to the dual-ring rotary electrodes, between the DC voltageand pulse voltage, in order that a control is performed more stably.

In this embodiment, there is provided an automatic switching device 630that automatically switches the kind of the voltage to be applied to thedual-ring rotary electrodes, between the DC voltage and pulse voltage,so that the control is more stably performed.

FIG. 18 is an explanatory view of an embodiment of a method of thepresent invention for performing contact-discharge truing/dressing whilemeasuring the truing amount.

In this embodiment, a displacement sensor 37 for measuring the positionsof the side surfaces of the electrodes is disposed on the side of theelectrode side-surfaces, and truing/dressing is performed whilemeasuring the truing amount.

As shown FIG. 19, the displacement sensor 37 may be disposed in the mainbody 701 of the truing device.

Disposing a displacement sensor for measuring the positions of the sidesurfaces of the electrodes, on the side of the electrode side-surfacesin this manner, allows the truing amount by the contact-dischargetruing/dressing to be monitored. When this is applied to in-processtruing/dressing, it is possible to perform working while correcting thetool path.

FIG. 20 is an explanatory view of an embodiment of a contact-dischargetruing/dressing method according to the present invention that isapplied to in-process truing/dressing, and that is executed whilecorrecting the tool path based on the truing amount.

In FIG. 20, reference numeral 801 designates a correcting device fortruing path based on the truing amount upon receipt of an output signalfrom the sensor 37, and reference numeral 802 designates anumerical-control moving table loaded with a workpiece 803.

This embodiment is applied to in-process truing/dressing, and isarranged to perform contact-discharge truing/dressing while correctingthe tool path based on the truing amount.

However, when truing/dressing is performed by the above-describedmethod, an electrode material adheres to the projecting portions(portions where deflections are large) of the trued/dressed grindstone,and consequently, there is possibility that a phenomenon occurs in whichthe electrodes continue to retreat. To solve this problem, it iseffective to have the following arrangement.

FIG. 21 is a representation of an embodiment of a truing/dressing deviceaccording to the present invention that has a dual-ring rotaryelectrodes inside which a conventional grindstone (nonconductivegrindstone) is disposed.

As shown in FIG. 21, a conventional grindstone (nonconductivegrindstone) 912 is disposed inside dual-ring rotary electrodes 910comprising an electrode inner ring 913, an insulating layer 914, and anelectrode outer ring 915 that are rotated by the rotating main shaft 911of the dual-ring rotary electrodes 910.

With these features, even if the electrode material adheres to theprojecting portions (portions where deflections are large) of thetrued/dressed grindstone 100 as a result of performing truing/dressing,the adhered electrode material can be reliably removed by theconventional grindstone (nonconductive grindstone) 912 disposed insidethe dual-ring rotary electrodes.

FIG. 22 is a representation of an embodiment of a truing/dressing deviceaccording to the present invention that has a dual-ring rotaryelectrodes outside which a conventional grindstone (nonconductivegrindstone) is disposed.

As shown in FIG. 22, a conventional grindstone (nonconductivegrindstone) 925 is disposed outside dual-ring rotary electrodes 920comprising an electrode inner ring 922, an insulating layer 923, and anelectrode outer ring 924 that are rotated by the rotating main shaft 921of the dual-ring rotary electrodes 920.

With these features, even if the electrode material adheres to theprojecting portions (portions where deflections are large) of thetrued/dressed grindstone 100 as a result of performing truing/dressing,the adhered electrode material can be reliably removed by theconventional grindstone (nonconductive grindstone) 925 disposed outsidethe dual-ring rotary electrodes.

The present invention is not limited to the above-described embodiments.Various modifications may be made on the basis of the true spirit of thepresent invention, and these modifications are not excluded from thescope of the present invention.

As described above in detail, the present invention has effects asfollows.

-   (A) Truing/dressing of a superabrasive grindstone, especially a    superabrasive grindstone having a metal binder can be very simply    performed.-   (B) High-precision shape creating work can be achieved.-   (C) On-board truing/dressing can be performed by a dry grinding    machine.-   (D) Irrespective of whether a conductive grindstone or nonconductive    grindstone, truing/dressing with respect thereto can be performed by    the identical device.-   (E) A grindstone working surface with high circularity can be    attained.-   (F) Because of low wear of the electrodes, greater economy can be    achieved, and work environment can be conserved in a clean state.-   (G) A sharp V-shaped edge shape can be easily created.-   (H) The circularity of the grindstone can be monitored while    conducting truing/dressing. As a result, truing/dressing condition    that is appropriate for the occasion can be provided.-   (I) In in-process truing/dressing, working is performed while    correcting the tool path.-   (J) Even if the electrode material adheres to the projecting    portions (portions where deflections are large) of the trued/dressed    grindstone as a result of performing truing/dressing, the adhered    electrode material can be reliably removed by the conventional    grindstone (nonconductive grindstone) disposed inside or outside the    dual-ring rotary electrodes.

INDUSTRIAL APPLICABILITY

The contact-discharge truing/dressing method and the device thereforaccording to the present invention are capable of very simply conductingtruing/dressing of a superabrasive grindstone, especially asuperabrasive grindstone having a metal binder. The presentcontact-discharge truing/dressing device is, therefore, suitable for acontact-discharge device capable of high-precision shape creating work.

1. A contact-discharge truing/dressing method, comprising: bringing arotated conductive grindstone to be trued/dressed into contact with apair of electrodes to which a DC voltage or pulse voltage is applied,and subjecting said conductive grindstone to be trued/dressed to anintermittent truing/dressing by contact discharge produced whenopening/closing a circuit comprising a positive electrode, electrodechips on the positive electrode side, a grindstone binder, electrodechips on a negative electrode side, and the negative electrode, whereinparts of side surfaces of dual-ring rotary electrodes insulated by aninsulator are used as a pair of electrodes.
 2. A contact-dischargetruing/dressing method, comprising: bringing a rotated nonconductivegrindstone to be trued/dressed into contact with a pair of electrodes towhich a DC voltage or pulse voltage is applied, and subjecting saidnonconductive grindstone to be trued/dressed to an intermittenttruing/dressing by contact discharge produced when opening/closing acircuit comprising a positive electrode, electrode chips, and a negativeelectrode, wherein parts of side surfaces of dual-ring rotary electrodesinsulated by an insulator with a thickness of several hundred μm or lessare used as a pair of electrodes.
 3. A contact-discharge truing/dressingmethod according to claim 1 or 2, wherein said contact-discharge isperformed in an environment of a liquid, a mist, or the air.
 4. Acontact-discharge truing/dressing method according to claim 1 or 2,wherein, in order to remove initial rotational deflections of the sidesurfaces of said dual-ring rotary electrodes, after the side surfaces ofsaid electrodes have been ground by said grindstone to be trued/dressedwithout applying a voltage between said electrodes, truing/dressing isstarted with a voltage applied between said electrodes.
 5. Acontact-discharge truing/dressing method according to claim 1 or 2,wherein a grindstone is disposed inside said dual-ring rotaryelectrodes, and wherein adherents of the electrode material adhering tosaid grindstone to be trued/dressed are removed for every discharge. 6.A contact-discharge truing/dressing method according to claim 1 or 2,wherein a grindstone is disposed outside said dual-ring rotaryelectrodes, and wherein adherents of the electrode material adhering tosaid grindstone to be trued/dressed are removed for every discharge. 7.A contact-discharge truing/dressing device wherein a rotated conductivegrindstone to be trued/dressed is brought into contact with a pair ofelectrodes to which a DC voltage or pulse voltage is applied, andwherein said conductive grindstone to be trued/dressed is subjected toan intermittent truing/dressing by contact discharge produced whenopening/closing a circuit comprising a positive electrode, electrodechips on the positive electrode side, a grindstone binder, electrodechips on a negative electrode side, and the negative electrode, saidcontact-discharge truing/dressing device comprising: (a) dual-ringrotary electrodes insulated by an insulator; and (b) a pair ofelectrodes of said positive electrode and said negative electrode andcomprising parts of side surfaces of said dual-ring rotary electrodes.8. A contact-discharge truing/dressing device wherein a rotatednonconductive grindstone to be trued/dressed is brought into contactwith a pair of electrodes to which a DC voltage or pulse voltage isapplied, and wherein said nonconductive grindstone to be trued/dressedis subjected to an intermittent truing/dressing by contact dischargeproduced when opening/closing a circuit comprising a positive electrode,electrode chips, and a negative electrode, said contact-dischargetruing/dressing device comprising: (a) dual-ring rotary electrodesinsulated by an insulator with a thickness of several hundred μm orless; and (b) a pair of electrodes of said negative electrode and saidpositive electrode and comprising parts of side surfaces of saiddual-ring rotary electrodes.
 9. A contact-discharge truing/dressingdevice according to claim 7 or 8, further comprising a drive mechanismfor driving said dual-ring rotary electrodes in the rotating shaftdirection thereof.
 10. A contact-discharge truing/dressing deviceaccording to claim 9, further comprising a structure capable of applyinga voltage between dual-ring rotary electrodes with mutually differentdiameters.
 11. A contact-discharge truing/dressing method, comprisingobtaining, using the device according to claim 9, a predetermined shapeof the edge of a grindstone, by providing said electrodes with a feed inthe rotating shaft direction thereof in state in which a predeterminedangle is formed between the rotating shaft of said electrodes and thatof said grindstone to be trued/dressed.
 12. A contact-dischargetruing/dressing method, comprising disposing, using the device accordingto claim 9, a drive device for said dual-ring rotary electrodes, on anumerical-control moving table having a crosswise movement mechanism ana rotational mechanism, to thereby perform high-precision formtruing/dressing.
 13. A contact-discharge truing/dressing method,comprising inserting, using the device according to claim 9, acontact-discharge current limiting resistor and a current detector onthe side of the power supply circuit of said device so as to be inseries with said pair of electrodes, whereby the feed speed of saiddual-ring rotary electrodes in the rotating shaft direction thereof isnumerically controlled so that the power consumption between saidelectrodes becomes the maximum when the contact-discharge current takeson the peak value I_(p).
 14. A contact-discharge truing/dressing method,comprising disposing, in the contact-discharge truing/dressing deviceaccording to claim 9, a displacement sensor for measuring the positionsof the side surfaces of said electrodes, on the side-surface side ofsaid electrodes to thereby perform truing/dressing while measuring thetruing amount.
 15. A contact-discharge truing/dressing device accordingto claim 9, further comprising a displacement sensor for measuring thepositions of the side surfaces of said electrodes, said displacementcensor being provided on the side-surface side of said electrodes.
 16. Acontact-discharge truing/dressing device according to claim 7 or 8,further comprising a grindstone disposed outside said dual-ring rotaryelectrodes.
 17. A contact-discharge truing/dressing device according toclaim 7 or 8, further comprising a structure capable of applying voltagebetween dual-ring rotary electrodes with mutually different diameters.18. A contact-discharge truing/dressing method, comprising obtaining,using the device according to claim 7 or 8, a predetermined shape of theedge of a grindstone, by providing said electrodes with a feed in therotating shaft direction thereof in a state in which a predeterminedangle is formed between the rotating shaft of said electrodes and thatof said grindstone to be trued/dressed.
 19. A contact-dischargetruing/dressing method, comprising disposing, using the device accordingto claim 7 or 8, a drive device for said dual-ring rotary electrodes, ona numerical-control moving table having a crosswise movement mechanismand a rotational mechanism, to thereby perform high-precision formtruing/dressing.
 20. A contact-discharge truing/dressing method,comprising inserting, using the device according to claim 7 or 8, acontact-discharge current limiting resistor and a current detector onthe side of the power supply circuit of said device so as to be inseries with said pair of electrodes, whereby the feed speed of saiddual-ring rotary electrodes in the rotating shaft direction thereof isnumerically controlled so that the power consumption between saidelectrode becomes the maximum when the contact-discharge current takeson the peak value I_(p).
 21. A contact-discharge truing/dressing methodaccording to claim 20, wherein the mean value I_(m) and die peak valueI_(p) of the output from said current detector are acquired at a periodof one or more revolutions of said grindstone to be trued/dressed, andwherein truing/dressing is performed while estimating the circularity ofsaid grindstone to be trued/dressed, based on the value of I_(m)/I_(p).22. A contact-discharge truing/dressing method according to claim 21,wherein, based on said estimated circularity of said grindstone to betrued/dressed, the magnitude of contact-discharge power consumptionE-I_(p)/2 is automatically adjusted by a numerical control or anautomatic control to thereby perform high-precision truing/dressing. 23.A contact-discharge truing/dressing method according to claim 21,wherein, when the estimated circularity of said grindstone to betrued/dressed becomes a predetermined value or less, the truing/dressingis automatically ended.
 24. A contact-discharge truing/dressing methodaccording to claim 20, wherein, in order that a control is performedmore stably, the kind of the applied voltage to said dual-ring rotaryelectrodes is automatically switched between said DC voltage and pulsevoltage.
 25. A contact-discharge truing/dressing method, comprisingdisposing, in the contact-discharge truing/dressing device according toclaim 7 or 8, a displacement sensor for measuring the positions of theside surfaces of said electrodes, on the side-surface side of saidelectrodes to thereby perform truing/dressing while measuring the truingamount.
 26. A contact-discharge truing/dressing method according toclaim 25, wherein said contact-discharge truing/dressing method isapplied to in-process truing/dressing to thereby execute said methodwhile correcting the tool path based on the truing amount.
 27. Acontact-discharge truing/dressing device according to claim 7 or 8,further comprising a displacement sensor for measuring the positions ofthe side surfaces of said electrodes, said displacement censor beingprovided on the side-surface side of said electrodes.
 28. Acontact-discharge truing/dressing device according to claim 7 or 8,further comprising a grindstone disposed inside said dual-ring rotaryelectrodes.